1. Field of the Invention
The present invention relates to a magnetic disc apparatus having a dehumidifying means for removing the moisture in the apparatus.
2. Description of the Prior Art
A conventional magnetic disc apparatus is shown in FIG. 1, in which the magnetic disc apparatus consists of a disc to be rotated, a head which is held in close vicinity to the recording surface of the disc, an actuator to let the head travel on the disc in the radial direction thereof and the like (none of them is shown in the drawings), installed in a container 1. At an appropriate position in the container 1, a vent 2 is provided for allowing the outside air to flow into the container 1, in order to temper the change in pressure in the container 1.
The moisture in the outside air, however, also flows into the container 1 from the vent 2, which results in an increase in the humidity in the container 1. And if the disc is made to stop rotating at such high humidities in the container 1 and the head is made to contact the disc, the head and the disc sometimes absorb each other to bring about troubles.
Therefore, in a conventional manner, the humidity in the container 1 is restrained from increasing by installing an absorber 15 in the container 1 which is an absorbent case 15a charged with a silica gel 15b, a siliceous absorbent, inside, for example, and by absorbing the moisture entering the container 1 with the silica gel 15b in the absorber 15. In this connection, the absorbent case 15a is provided with an opening 15c for regulating the absorbing speed, which controls the absorbing speed lest the humidity in the container 1 should excessively be low, while the moisture is absorbed by the silica gel 15b through the opening 15c. (See, for example, "The Tribology of Magnetic Records", a paper for the 46th. Meeting of the Applied Magnetics Society of Japan, a corporation aggregate, p. 17.)
The silica gel 15b, however is porous and the surface area per unit weight is very large, and while its amount of moisture-absorbing per unit weight will increase substantially in proportion to the increase in humidity as long as the structure of the silica gel 15b is kept gelatinous, as apparent from FIG. 2 showing the relationship between the amount of moisture-absorbing per unit weight and the humidity, the moisture-absorption by the silica gel 15b tends to be saturated when the humidity is high enough and the moisture-absorption by the silica gel 15b has sufficiently advanced to increase the moisture content in the silica gel 15b. (See, for example, "Kagaku Kohgaku Binran" [A Handbook of Chemical Engineering, in English], the 1978 revised 4th. edition, published by Maruzen Company Limited, p. 854.)
However, such a conventional apparatus has problems. For example, in the case where the moisture-absorption by the silica gel 15b in the absorber 15 has reached its saturation, the moisture in the container 1 cannot be absorbed by the silica gel 15b even when the humidity in the container 1 excessively increases. In addition, the amount of the moisture-absorption cannot be controlled on account of the size of the opening 15c for regulating the absorbing speed normally being fixed, which results in that it is not possible to control the humidity in the container 1 correspondingly to that in the outside air in such a case where the humidity in the outside air is very high and much moisture flows into the container 1 to bring about a slight insufficiency of the prevention of moisture in the container 1, for example.